Automatic telephone system



Aug. 7, 1928.

J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM Filed Feb. 5, 1921 Ear/152;;

Patented Aug. 7, 1928.

UNITED STATES PATENT OFFICE.

JOHN E. GARDNER, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS,TO AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OFDELAWARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed February 5, 1921. Serial No. 442,743.

The present invention relates in general to automatic telephone systemsbut is more particularly adapted to be used in small automatic exchangeswhich are known commercially as private automatic exchanges. Inexchanges of this character certain special features are usuallyprovided for the convenience of the subscribers among which probably themost important is known as conference calling. This is an arrangement toenable three or more parties to be telephonically connected together atthe same time. There are several ways for accomplishing this result themost common of which is to have each partyv desired in the conferencenotified either by means of a code call or by communicating with eachone separately and telling him to call the conference number. ,If theconference code call is rung, it will, ofcourse, be apparent that allthe subscribers who are usually included in the conference willthen callthe conference number. However if the party setting up the conferencedesired to include only certain subscribers therein he would call eachone separately and instruct him to call the conference number at anypredetermined time.

Hitherto, in arrangements of this nature it has been more or lessimpossible to protect the conference number from intrusion and anysubscriber who desired, knowing that a conference was being held mightlisten to it. Also any party was able to set up a conference. Thesearrangements are more or less undesirable.

A feature of the present invention is therefore to provide a means forpositively.protecting the conference from intrusion when it is onceestablished.

Another object is to restrict conference calling so as to prevent allthe subscribers except important ofiicials of a company having a privateautomatic exchange from using the conference feature.

The particular manner in which these and other results are accomplishedwill be described fully hereinafter reference being had to theaccompanying drawings.

In the present case the invention has been shown applied to an isolatedprivate automatic exchange but it will of course be readily apparentthat it is not restricted to this use and may be used whereverconference calling is installed.

Referringnow to the drawings comprising a single sheet, in Fig. 1 isshown an automatic substation A, having a rotary line switch C of wellknown construction individual thereto. The line switch C in common witha plurality of other similar line switches have access to trunk linesleading to connector switches, one of these being shown at H. Theconnector switch H has access to local subscribers lines and theconference number. It is of the Strowger'type having 100 bank contactsarranged in ten 'I'OWS or levels. Bank contacts 150-153, in-

clusive, are the terminals of a called subscribers line the substationof which is shown at A. Bank contacts 141-144, inclusive, accessible tothe connector H are the terminals of the conference number which we willassume in the present case is the N o. 60. The relay 175 is common toall the connector switches and is associated with the conference number.I

Fig. 2 shows a certain manner of connect ing the test banks of the.local connectors such as H to secure rotary service.

Having described briefly the construction of the switches involved inthe invention a detailed explanation of their operation will now begiven. For this purpose it will be assumed that the subscriber atsubstation A desires to hold a conference with a number of othersubscribers. He will therefore remove his receiver and operate hiscalling device in accordance with the digits of the first subscribersnumber desired in the conference. When the subscriber answers thecalling subscriber will tell him that a conference isto be held and willthen hang up his receiver and in the same manner call the remainingsubscribers. Each one of the called subscribers will then in turn callthe conference number as will the calling subscriber atsubstation Aafter he has communicated with all the parties he desires in,

the conference. be described.

When the receiver is removed at substation A the line relay 16 of theindividual line switch C is energized over the line conductors 11 and 12in series. Upon energizing, relay 16 at armature 25 completes a Theseoperations will now circuit which includes the switching relay and thestepping magnet 17 in series and at its armature 21 connects the testwiper 29 to the above circuit at a point midway between the switchingrelay and the step ping magnet 17. The operation of the retary lineswitch now depends upon whether the trunk line with which the switchwipers 28%31, inclusive, are in engagement is or is not busy. If busy,there will be a ground potential upon the test contact engaged by testwiper 29. The switching relay 15 will be short circuited and thestepping magnet 17 being supplied with direct ground by way of the saidtest wiper will operate as a buzzer to advance the switch wipers step bystep in search of an idle trunk line. However, it will be assumed in thepresent case when the receiver 1 was removed at the calling substationthat the switch wipers of the line switch C were in engagement with thebank contacts shown in the drawings, and further that this trunk linewas idle. Under these circumstances immediately after the operation ofthe line relay 16 the switching relay 15 is energized in series with thestepping magnet. It may be stated at this time that the switching relay15 is of comparatively high resistance so as to prevent the operation ofthe steps ping magnet 17 at this time. Upon encrgizing, relay 15disconnects the incoming line conductors 11 and 12 of the substation Afrom the winding of the line relay 16 and from ground, respectively, andconnects them by way of armatures 20 and 23 and their front contacts,wipers 28 and 31, to the upper and lower windings of the line relay 5Oof the connector H.

The line relay will be energized over the calling subscribers line loopand upon operating, completes a circuit of the slow acting release relay51. Relay 51 upon at tracting its armaturcs, prepares the circuits ofthe connector H for operation at armature 73 and at armature 72 placesground on release trunk conductor 93 thcreby establishing a holdingcircuit which extends by way of test contact 36, test wiper 29, armature21 and its front contact, through the winding of the switching relay15,and through the winding of the stepping magnet 17 to battery. It willbe understood that the above traced holding circuit is completed beforethe slow acting line relay 16 has had time to deenergize. A branch ofthe holding circuit also extends by way of the private normal conductor40 to multiply connected test contacts in the banks of local connectorswitches, such as the switch H, which have access to the line of thesubstation A, whereby said line is protected from intrusion in the usualmanner.

The calling subscriber may now operate his calling device in accordancewith the first digit of the desired subscribers number thereby producinga series of interruptions in the line circuit of the line relay 50. Theline relay 5O retracts its armature a plu rality of times in response tothese interruptions each time sending an impulse of current over thefollowing path: ground by way of armature 70 and its back contact,armature 73 and its front contact, off normal springs 80 and 81, windingof the vertical magnet 61, and the winding of the slow acting seriesrelay 55 to battery. The above is the circuit over which the firstimpulse to the vertical magnet is sent but upon the first vertical stepof the shaft the off normal springs are shifted and the remainingvertical impulses travel over a different circuit which includes theoif-normal springs 80 and 82 and armature 103 and its front contact,(relay 55 being now in an operated position). The vertical magnet 61operates to raise the switch wipers 135-138, inclusive, step by stopuntil they are placed opposite the level of bank contacts in which isterminated the line of the substation A, The slow acting relay 55 isenergized in series with the vertical magnet, maintains its armatureattracted throughout the vertical operation of the switch, and shortlyafter its termination deenergizes transferring the operating circuit tothe rotary magnet 62.

The calling subscriber may now call the final digit of his desiredsubscriber-ls number. As before, a series of interruptions are producedin the line circuit of relay 50 which retracts its armature a pluralityof times in response thereto. A series of impulses are thereby sent tothe rotary magnet 62 over a circuit extending from ground by way ofarmature and its back contact, armature 73 and its front contact, offnormal springs and 82, armature 108 and its back contact, winding of theslow acting series relay 56, armature 96 and its back contact, baclrcontact and armature 113, and through the winding of the rotary magnet62 to battery. Magnet 62 operates to rotate the switch wipers step bystep until they are placed in engagement with the bank contact setassociated with the line of substation A which we will assume'are thebank contacts 150-153, inclusive. The slow acting relay 56 which isenergized in series with the rotary magnet operates to connect the testwiper 136 to the upper winding of the test relay 5 f. The furtheroperation of the. connector H depends upon whether or not the line ofthe substation A is or is not busy. If busy, there will be a groundpotential present on the test contact 151 engaged by test wiper 136.Assuming this to be the case a circuit is completed from ground on testcontact 151, by way of said test wiper, normally closed springscontrolled by relay 57, amature 105 and its front contact, resistance R,normally closed springs controlled by relay 52, and through the upperwinding of the test relay 54 to battery. Upon energizing, this latterrelay at armature 95 establishes a holding circuit for itself and atarmature 98 places the busy tone from the busy machine on the lowerheavy talkin conductor whereby the calling subscriber is notified thatthe line of the substation A is busy. Upon hearing this tone the callingsubscriber will replace his rea-eiver upon the switchhook therebyinitiating the release of the connector H and the line switch C in thewell known manner.

It will now be assumed that the line of the subscriber at substation Awas idle when the wipers of the connector H are rotated into engagementtherewith. Then, following the deenergization of the slow acting relay56, a circuit is completed extending from ground on release trunkconductor 93, normally closed springs controlled by relay 55, armature95 and its back contact, resting contact of spring 123 and the saidspring, through the lower winding of the switching relay 57, backcontact and armature 105, normally closed springs controlled by relay57, test wiper 136, test contact 151, winding of the switching relay 170of the line switch 0, and thence through the winding of the steppingmagnet 17 2 to battery. Relays 57 and 170 energize over this circuit.However, due to a mechanical interlocking controlled by the armature ofthe line relay, the switching relay 170 is only energized suflicientlyto disconnect the line of the substation A from its normal battery andground connections in the line switch C. Relay 57. upon energizing,establishes a locking circuit for itself at armature 111, places directground on test contact 151 at armature 112, and at armature 115completes the ringing circuit. Ringing current is then intermittentlyprojected over the line of the substation A until the subscriber thereatremoves his receiver. WVhen this occurs a path for direct current isprovided over the called subscribers line loop for the upper winding ofthe ring cut off relay 52. The latter relay upon energizing, locksitself at armature 87 and at arniatures 86 and 88 breaks the ringingcircuit of the called subscriber and at the front contacts of thesearmatures finally completes the talking connection. Talking battery isfurnished to the calling subscriber from the windings of the line relay50 and to the called subscriber from the windings of the back bridgerelay 54. The subscriber at substation A will now inform the calledsubscriber at substation A that a conference is to be held and give himany other information necessery after which he will replace his receiverupon the switchhook. By this last operation the contrunk line except thelast are tied together and those oft-he last trunk line left open. Thus,as may be seen from Fig. 2, if the up per test contact of any one exceptthe last trunk in the group be grounded, as is the case when one isbusy, this ground will also be present on the lower test contact while,if the last trunk line be busy, ground will only be present on the uppertest contact.

From the above explanation it will be seen that ordinary individuallines have their test contact left untied.

The operation of the connector H when used in this case will now bebriefly described. For this purpose it will be assumed that the callingsubscriber at substation A has operated his calling device in accordancewith the digits of the number associated with the group of trunksmentioned with regard to Fig. 2. Should this first line be busy acircuitwill be completed by way of test wiper 136 for the test relay 54.A new circuit will also be completed extending from test contact engagedby test wiper 137, there being a ground present on the test contactengaged by this wiper as it is tied to the test contact engaged by testwiper 136, armature 107 and its back contact, armature 97 and its frontcontact, armature 104 and its back contact, Winding of the steppingrelay 53, and thence through the winding of the slow acting relay tocircuit. Relay 53 upon operating, establishing a locking circuit foritself at armature 91 and at armature 9O completing the rotary magnetcircuit. Relay 55 upon'energizing, serves to maintain the test wiper 136in connection with the test relay 54. Magnet 62 operates to rotate thewipersinto engagement with the next trunk line and to break the lockingcircuit of the stepping relay 53 at armature 104, which relaydeenergizes opening the circuit of the rotary magnet whichdeenergizesalso. If this next trunk line is busy the stepping relay 53 will beagain energized to complete the rotary magnetcircuit. This alternateoperation of the stepping relay 53 .and the magnet 62 will continue totake place until an idle trunk is found or the switch wipers arerotatedinto engagement with the bank cont-act set associated with the lasttrunk line in the group. In the latter case relay 53 will not beenergized for the reason that the test banks are not tied together inthis case. The relay 54, however, will remain energized and serves totransmit the busy signal to the calling subscriber.

The calling subscriber at substation A may in the manner just describedcall all the other subscribers desired in the conference after which hewill himself connect with the conference number. The latter operationwill now be briefly described. When the receiver is removed atsubstation A the individual line switch C operates in the usual mannerto select an idle trunk line terminating in a connector switch which wewill assume is the connector shown at H. The line and release relays and51 ener ize as be fore described and with the same results.

lVhen the calling device is operated for the first digit of theconference number, namely, 6, six interruptions are produced in thecircuit of the line relay 50 which operates in response thereto. At eachretraction of its armature an impulse of current is sent to the verticalmagnet 61 in series with the slow acting relay 55. The vertical magnet(31 operates to raise the switch wipers step by .step until they areplaced opposite the sixth level of bank contacts. The slow acting relay55 is energized in series with the vertical magnet and remains sothroughout the vertical operation of the switch and at the terminationthereof deenergizes and transfers the operating circuit to the rotarymagnet 62.

The calling subscriber may now call the second digit of the conferencenumber namely the digit 0. Ten interruptions are thereby produced in theline circuit of relay 50 which deenergizes a corresponding number oftimes. At each deenergization, an impulse of current is sent to therotary -magnet 62 in series with the slow acting relay 56. Magnet 62operates to rotate the switch wipers 135-138, inclusive, into engagementwith the tenth set of contacts in the sixth level which we will assumeare bank contacts 1l11ll, inclusive. The springs 117, 119, 121, 123 and125 are cam springs which are adapted to be shifted by the cam on theswitch shaft when the switch wipers are rotated into engagement with theconference number 60. The slow acting relay 56 is energized in serieswith the rotary magnet and operates to connect the test wiper 136 to thetest relay 5. The conference number will not however be busy at thistime for the reason that even though the test contacts are multipled inthe usual manner the switching relay of each connector when operating onthe conference number does not place ground on the test wipers similarto the wiper 136 as ground is removed by the operation of cam springssimilar to spring 121. Then following the deenergizaticn of the slowacting relay 56 a circuit is completed extending from ground ondiscriminating trunk conductor 127, working contact of cam spring 123and the said spring, lower winding of the switching relay 57, backcontact and armature 105, normally closed springs controlled by relay57, test contact 142, and through resistance R to battery. Relay 57energizes over this circuit and upon operating establishes a lockingcircuit for itself at armature 111, at armature 114 prepares a point inthe operating circuit for the associated conference relay 175, and atarmature 115 prepares a point in'the talking connection to thesubscriber at substation A. Upon the cam spring 119 being shifted intoengagement with its working contact by the operation of the switch shafta cir cult is completed from ground by way of working contact and spring119, upper winding of the ring out off relay 52, front contact andarmature 113, through the winding of the rotary magnet 62 to battery.Relay 52 energizes over this circuit, locks itself at armature 87, andat armatures 86 and 88 completes the talking connection to the line ofthe subscriber at substation A. It will be seen that relay 57 uponoperating, does not place ground on test wiper 136 for the reason thatthe cam spring 121 is V out of engagement with its resting contact.

It may be noted also that unless the parties have ground on thediscriminating trunk of their associated line switch the switching relay57 or a similar relay in the associated connector switch will not beenergized on the conference number. Therefore conference service isrestricted to those subscribers whose line switches are connected in themanner shown in the line switch 0 having the armature 22 or similararmatures connected to ground. Should a subscriber not entitled toconference service attempt to connect with the conference number he willbe unable to do so. A restricted service subscriber will not have anyground present on the discriminating trunk so upon operating a connectorwhich, for the purposes of description is assumed to be the connector H,into engagement with the conference number no circuit will be completed.for the switching relay 57 or a similar relay. A circuit is theneffective extending from ground by way of working contact of spring 119and the said spring, back con tact and armature 110, through resistanceR and upper winding of the test relay 5% to battery. Relay 54:, uponenergizing, at armature 98 places the busy tone on the callingsubscribers line thereby informing him that he is not allowed conferenceservice.

In the same manner as above described all the subscribers called by thesubscriber at substation A will call the conference numher and beconnected thereto provided of course they are entitled to conferenceservice. When the last subscriber that the lllll iii armature 114 andits front contact, and. through the winding of the common con-' ferencerelay 175 to battery. Upon energizing, relay 175 at armature 176'establishes a locking circuit for itself which extends to the releasetrunk of all the connector switches brought into engagement with theconference number and at armature 177 places ground on the multiplyconnected test contacts .of the conference number in the banks of alllocal connector switches.

In this manner any'subscriber now calling the conference number eventhough he should have ground connected to h1s d1scriminating conductorwill not be able to obtain connection with the conference for the reasonthat there will be ground present on the test contacts of the conferencenumber and the associated connector switch used by this subscriber willoperate to transmit the busy tone to him thereby notifying him that aconference is being held and the conference number is inaccessible tohim at this time.

Conversation may now take place between all the parties connected in onthe conference and when this is terminated each party will replace hisreceiver upon the switchhook and by this operation will release hisassociated connector switch in the usual manner. The last party to hangup will cause the relay 175 associated with the conference number todeenergize and ground will be removed from the multiply connected testcontacts of the conference number and all the apparatus will be returnedto its normal condition.

Having fully described and ascertained the features of the inventionwhat is considered to be new and desired to have protected by LettersPatent will be pointed out in the appended claims.

lVhat I claim as my invention is:

1. In a telephone system, a calling subscribers line, an automaticswitch associated therewith, called lines accessible thereto, a callingdevice under the control of said calling subscriber for operating saidswitch into engagement with one of said called lines without making thesame busy, and means individual to said automatic switch and responsiveto the reoperation of said calling device for preventing anotherconnection be ing established with the connected line.

2. In a telephone system, a calling. sale scribers line,-an automaticswitch associated therewith, called lines accessible thereto. a

calling device under the control of said calling subscriber foroperating said switch into engagement with one of said called lineswithout makii'ig the same busy, and a relay individual to said switchand energized in response to the reoperation of said calling device forapplying a busy potential to said called line. I

3. In a telephone system, an automatic connector switch operable forcompleting connections to called lines, means in said connectorautomatically responsive to the completion of a connection for makingthe connected called line busy, and means in said connectorautomatically responsive to' the completion'of a connection with aparticular called line formaintaining the'con- ,nected called line inidle condition.

4.111 a telephone system, an automatic connector switch operable for.completing connections to called lines, means inv said connectorautomatically responsive to the completion of a connection for makingthe connected called line busy, means in'said connector automaticallyresponsive to the completion of a connection with a particular calledline for maintaining the connected called line in idle condition, andmeans controlled at the option of the calling subscriber in case saidlast mentioned line is connected with for making the same busy.

5. In a telephone system, two lines, an automatic connector switchoperable to complete a connection to either of said lines, and means insaid connector automatically responsive to the completion of aconnection for making the line busy only in case the line called is aparticular one of said lines.

6. In a telephone system, two lines, an automatic connector switchoperable to complete a connection to either of said lines, means in saidconnector automatically responsive to the completion of a connection formaking the line busy only in case the line called is a particular one ofsaid lines,

and means operable thereafter by the call ing party in case the otherline has been connected with for making such line busy.

7. In a telephone system, a conference line, automatic switches operableeach by a different calling party to connect with said line, saidswitches being arranged to connect with said line without making thesame busy' in order to permit each connection to ferent calling party toconnect with said line,

said switches being arranged to connect with said line without makingthe same busy in order to permit each connection to be made before theprevious connections are released, and means in each switch controlledat the option of the party using the same for making the conference linebusy in order to prevent the establishment of any more connectionstherewith, said means comprising a busying relay for the said conferenceline, and a plurality of conductors connected to said relay in multipleand extending each to a different one of said switches.

9. In a telephone system, subscribers lines of two classes, a conferenceline, automatic switches common to said subscribers lines and operableeach by a different calling subscriber to connect with said conferenceline, said switches being arranged to connect with said lines withoutmaking the same busy in order to permit each connection to be madebefore the previous connections are released, and service restrictingmeans whereby the subscribers whose lines are in a particular class areprevented from operating one of said switches to connect w th theconference line.

10. In a telephone system, subscribers lines of two classes, aconference line, automatic switches common to said subscribers lines andoperable each by a different calling subscriber to connect with saidconferenceline, said switches being arranged to connect with said lineswithout making the same busy in order to permit each connection to bemade before the previous connections are released, and servicerestricting means whereby the subscribers whose lines are in one classare always prevented from connecting with the conference line, whereasthe subscribers whose lines are in the other class may only be preventedfrom connecting with the conference line by a subscriber who haspreviously established such a connection.

Signed by me at Chicago, Illinois, this 21st day of January, 1921.

JOHN E. GARDNER.

